This invention relates to a vehicle occupant protection air bag module used for restraining a vehicle occupant in his or her seated position in the event of a collision and, more particularly, to an air bag module, in which a retainer case accommodating an air bag is mounted adjacent to a passenger compartment wall.
Air bag modules are recently used as a vehicle occupant protector for restricting a vehicle occupant's inertial forward movement at the time of a collision and thereby preventing secondary striking of the occupant against the front window glass, instrument panel, etc. In such air bag modules, an air bag is quickly inflated and deployed toward the vehicle occupant at the time of a collision by causing gas issued under high pressure from a gas generator to be introduced into it, thus receiving the occupant tending to be moved forwardly. The air bag has an open end portion secured to a retainer case, and normally it is accommodated in a compactly folded state in the retainer case.
The retainer is typically vessel-like and open at one end, and it is mounted on a steering wheel, an panel, etc. located ahead of the vehicle occupant such that the open end faces the passenger's compartment. This means that the retainer case is disposed adjacent to a passenger's compartment wall.
A gas generator or inflator is secured to the end of the retainer opposite the open end thereof, and a portion of the retainer case on the side, to which the inflator is secured, is supported by the vehicle body.
In this vehicle occupant protection air bag, the retainer case is a one-piece molding, such as shown in U.S. Pat. No. 4,842,300.
In such air bag module as above, a reaction force of issuance of gas under high pressure is applied to the inflator during inflation and deployment of the air bag. Therefore, the portion of the retainer case, to which the inflator is secured, should have a sufficiently high mechanical strength. Moreover, if the retainer case is deformed by the internal gas pressure, the air bag may fail to be deployed to a designated shape. Therefore, a portion of the retainer case which is subject to high pressure, i.e., a portion in the vicinity of the inflator, should have a sufficiently high rigidity.
In the meantime, it is prescribed by regulation that a passenger's compartment wall, for instance an instrument panel surface, be provided with a predetermined impact energy absorption performance. This means that the air bag module should be installed on the instrument panel without possibility of spoiling the impact energy absorption performance of the instrument panel. This means that a portion of the retainer case which is adjacent to the instrument panel surface can be readily deformed.
This means that an air bag module which is disposed adjacent to a passenger's compartment wall is required to have a retainer case of varied rigidity. With the prior art retainer which is formed as a one-piece molding, however, it is difficult to meet such a requirement for it is difficult to vary the rigidity partially.
Moreover, it is difficult to secure the stem of the air bag to a retainer case of the one-piece structure. More specifically, the retainer case and air bag are both open at one end, and therefore if it is intended to mount them face to face, their inside is not perfectly shielded from the outside. The mounting, therefore, has to be made in groping-about manner. Moreover, if the air bag stem is secured in several portions, cracks may be produced in the secured portions by the pressure of inflation of the air bag. Therefore, the stem has to be secured over the entire circumference. Usually, the air bag stem is retained by a plate or the like, and its entire circumference is supported by the retainer case. This requires such a plate or the like and also an operation of securing the plate or the like to the retainer case.